VAN 211: Veterinary Histology and Embryology (2+2)

SPECIES DIFFERENCE

• The thickness of the skin varies with age, sex species and body region. The Ox has the thickest skin and sheep has the thinnest skin. It is thickest on the back and on the extensor surfaces of limbs than on the belly and flexor surfaces. The skin is very thick on the tail of the horse, on the dewlap of the Ox and on the ventral aspect of the neck of the pig.
• The wattles of the goat are appendages consisting of skin and subcutis. They include a striated muscle, a bar of elastic cartilage, vessels and nerves.
• The tip of the nose, foot pads and all muco-cutaneous junctions in all animals are devoid of hair. The hair root are set vertically in sheep and obliquely in all other animals. The medulla of the hair is lacking in the wool, hairs of ungulates and the hair of human scalp.
• The hairs are evenly distributed in horse and ox and occur in groups in dog, cat and pig. There is usually three hairs in a group. Of which, one is the main hair and is larger than the other two. In carnivores, each of these three hairs is surrounded by six to twelve wool hairs, the follicles of which branch off form the follicle of the main hair and thus a whole bundle of hairs may project form a common follicular opening.
• In tactile or sinus hairs, the connective tissue sheath is well developed and a blood sinus lined by endothelium occurs between the outer and inner layers of dermal sheath. They are present in the lips, nostrils and eyes.
• Coarse hairs of great length occur in the mane of horse and the tail of the horse and ox.
• Sebaceous glands are large in the horse and dog while those of the pig are rudimentary. In ungulates two to six sebaceous glands empty into one follicle. Sebaceous glands are largest at muco-cutaneous junctions but are absent from footpad, hooves, claws, the planum naso labiale and teats of Ox and planum nasale of sheep, goats and carnivores.
• Sweat glands: In man the merocrine glands are distributed over the entire skin surface while the apocrine glands are restricted to a few areas such as axilla, in domestic animal. The apocrine glands make up the majority of tubular skin glands, in sheep, pig, cat and horse the secretory tubule is wound up (glomiform) whereas in the Ox, goat and dog, it is serpentine. In the cat, the glands are poorly developed and are present only in a few body areas (oral region, anus, lower jaw, foot pads).
• The epidermis shows a high degree of specialization in forming the hooves, claws and horns in the different domestic animals.